The present invention relates to a process and to an arrangement for separating solid, sludge-like constituents and dissolved constituents from effluent and to a method of using semi-permeable filters in the form of tubing. Sludge-like constituents are also to be understood to include gel-like and colloidal media.
The purification of effluent, carried out generally in treatment plants, is effected via a sequence of process steps, such as, for example, neutralization of acid or alkaline effluents, pre-clarification in settling basins to remove solids as a pre-clarification sludge, biological purification using suspension of bacteria with the introduction of oxygen, and chemical clarification by coagulation of colloid-disperse substances.
A multiplicity of process steps is usually necessary for separating solid or sludge-like constituents from effluent. Thus, for example, the pre-clarification sludge initially obtained from the settling basin is subsequently concentrated in thickener basins, the thin sludge which settles in the thickener basin is dehydrated by means of centrifuges, after organic flocculating agents have been added, and only the thick sludge which has been separated off can be burned or converted into compost.
It is known from German Offenlegungsschrift No. 2,331,118 to dehydrate thick sludge, for example, with the aid of sludge filters in the form of tubing consisting of a synthetic fabric. However, raising the concentration of effluent or of sludges having a solids content of less than about 30% by weight, in particular less than 10% by weight, in an economical manner, using these devices is as a rule not possible. In these cases, a sufficiently thick filter cake, enriched in solids from the effluent, cannot be formed. In particular, when working without filter aids, the pores of the filters can be blocked even after a short time. Moreover, filters of a synthetic fabric are suitable only for separating macro-particles. The filtrate obtained is usually turbid and has a high solids content. Because of the high residual water content, the fabric tubing filled with sludge is less suitable for storage and/or combustion.